全文获取类型
收费全文 | 8157篇 |
免费 | 191篇 |
国内免费 | 170篇 |
专业分类
电工技术 | 173篇 |
综合类 | 329篇 |
化学工业 | 1348篇 |
金属工艺 | 701篇 |
机械仪表 | 1131篇 |
建筑科学 | 356篇 |
矿业工程 | 168篇 |
能源动力 | 745篇 |
轻工业 | 185篇 |
水利工程 | 147篇 |
石油天然气 | 584篇 |
武器工业 | 33篇 |
无线电 | 299篇 |
一般工业技术 | 671篇 |
冶金工业 | 449篇 |
原子能技术 | 190篇 |
自动化技术 | 1009篇 |
出版年
2024年 | 9篇 |
2023年 | 103篇 |
2022年 | 151篇 |
2021年 | 195篇 |
2020年 | 198篇 |
2019年 | 195篇 |
2018年 | 148篇 |
2017年 | 165篇 |
2016年 | 223篇 |
2015年 | 234篇 |
2014年 | 395篇 |
2013年 | 463篇 |
2012年 | 380篇 |
2011年 | 615篇 |
2010年 | 388篇 |
2009年 | 447篇 |
2008年 | 402篇 |
2007年 | 457篇 |
2006年 | 429篇 |
2005年 | 459篇 |
2004年 | 347篇 |
2003年 | 327篇 |
2002年 | 297篇 |
2001年 | 209篇 |
2000年 | 188篇 |
1999年 | 196篇 |
1998年 | 181篇 |
1997年 | 145篇 |
1996年 | 119篇 |
1995年 | 109篇 |
1994年 | 56篇 |
1993年 | 56篇 |
1992年 | 48篇 |
1991年 | 49篇 |
1990年 | 24篇 |
1989年 | 31篇 |
1988年 | 35篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 13篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有8518条查询结果,搜索用时 31 毫秒
101.
The onset of hydrodynamical instability induced by impulsive spin-down to rest in a cylinder containing a Newtonian fluid
is analyzed by using propagation theory. It is well-known that the primary transient swirl flow is laminar, but with initial
high velocities secondary motion sets in at a certain time. The dimensionless critical time Τc to mark the onset of instability is presented here as a function of the Reynolds number Re. Available experimental data indicate
that for large Re deviation of the velocity profiles from their momentum diffusion occurs starting from a certain time Τ≈4Τc. This means that secondary motion is detected at this characteristic time. It seems evident that during Τc⪯Τ⪯4Τc, secondary motion is relatively very weak and the primary diffusive momentum transfer is dominant. 相似文献
102.
. Murat Dogan B. Zü htü Uysal John R. Grace 《Chemical Engineering Communications》2004,191(4):566-579
Experiments were carried out in a half slot-rectangular spouted bed to investigate the effects of slot width and lower section basal angle on column hydrodynamics. Flow regimes, minimum spouting velocity, spouting and maximum pressure drops, and maximum spoutable bed height were determined for 4 mm diameter polyethylene particles. The results are compared with those for conventional cylindrical and rectangular spouted beds. Correlations for each hydrodynamic parameter are developed and compared with equations available in the literature. 相似文献
103.
Rheology of cementitious paste with silica fume or limestone 总被引:1,自引:0,他引:1
The rheological behaviour of cementitious pastes where cement has increasingly been replaced by densified silica fume (SF), untreated SF or limestone has been studied. The effect of SF on the flow resistance, taken as the area under the flow curve, was found to depend on the dispersing ability of the plasticizer as illustrated by pastes with naphtalene sulphonate-formaldehyde condensate (SNF) and polyether grafted polyacrylate (PA).The gel strengths increased with increasing SF replacement of cement independently of plasticizer type. The cementitious gel strength was, however, depending on the type of SF since pastes with densified SF developed lower gel strengths than pastes with untreated SF. This phenomenon was attributed to agglomerates in the densified SF which remained unbroken by the mixing and measurement sequence.Both flow resistance and gel strength decreased with increasing limestone replacement. Thus, silica fume may have an advantage over limestone filler as stabilizing agent for self-compacting concrete preventing segregation upon standing and reduced form pressure due to a more rapid gel formation. 相似文献
104.
The National Aeronautics and Space Administration's (NASA's) PS304 coating is a plasma spray deposited tribological coating with feedstock composed of NiCr, Cr2O3, Ag and BaF2-CaF2 powders. The effects of rounded BaF2-CaF2 particles on the gravity-fed flow characteristics of PS304 feedstock have been investigated. The BaF2-CaF2 powder was fabricated by water atomization using four sets of process parameters. Each of these powders was then characterized by microscopy and classified by screening to obtain 45-106 μm particles and added incrementally from 0-10 wt.% to the other constituents of the PS304 feedstock, namely nichrome, chromia and silver powders. The relationship between feedstock flow rate, measured with the Hall flowmeter, and concentration of fluorides was found to be linear in each case. The slopes of the lines were between those of the linear relationships previously reported using angular and spherical fluorides and were closer to the relationship predicted using the rule of mixtures. The results offer a fluoride fabrication technique potentially more cost-effective than gas atomization processes or traditional comminution processes. 相似文献
105.
针对新建的东北电力大学直流式低速风洞,介绍了其流场品质的测试方法和测试数据分析.包括:实验段风速、气流稳定性、流场均匀性、气流偏角、紊流度等五项,给出了测量的数值结果和相关参数的分布曲线,并确定了风机工作频率与气体流速之间的关系. 相似文献
106.
张洁 《安徽建筑工业学院学报》2009,17(4):81-82
论述了理性建筑的衰落及原因,阐述了非线性建筑的崛起对传统的暖通工程师的挑战,研究了非线性建筑的暖通工程师的工作方式和非线性建筑的特征下的暖通技术方法和措施. 相似文献
107.
一种基于自适应遗传算法的统一潮流控制器 总被引:1,自引:0,他引:1
黄江波 《重庆理工大学学报(自然科学版)》2010,(3):81-84
提出一种自适应遗传算法的智能控制策略,并将其应用于统一潮流控制器的多变量控制中.对3个通用的标准测试函数进行了优化,将其测试结果与简单遗传算法进行了比较.仿真结果表明:自适应机制提高了算法的搜索性能,与传统PI控制相比具有更强的动态性和鲁棒性。 相似文献
108.
油气长输管道在运行过程中易受到自然和人为因素的破坏,例如:洪水冲刷、防腐层老化、阴极保护失效、管道占压、不法分子打孔盗油(气)引起管体缺陷等,因此,管道抢修是管道运行管理工作中的重要组成部分。为了延长管道的使用寿命,避免停输抢修给企业造成不必要的经济损失,对不停输抢修技术在长输管道中的应用进行了研究,有效地降低了管道经营成本,对企业进行油气管道运行管理具有一定的借鉴指导意义。 相似文献
109.
综合分压配气和流量配气的特点和优势,设计了基于分压配气和流量配气原理的自动化配气控制系统,用于I类、II类隔爆型设备(d)和III类可燃性粉尘环境外壳保型设备(tD)的耐爆和传爆试验。经试验测试与比对:该系统可靠性、精确度、稳定性和重复性方面均满足GB 3836.2-2010防爆试验所规定的要求,并具有节省试验时间和试验气源的优点。 相似文献
110.
Esmail R Monazam 《Powder Technology》2004,139(1):89-97
In recent years, although an increasing number of literature have been devoted to circulating fluidized bed (CFB), the prediction of velocities over which different fluidization regimes exist is still difficult. In this study, a transient method was applied which readily allows one to identify operational features and critical transitions. The method is based on stopping the solids flow rate into the riser when riser is operating in fully dense transport regime. The analysis of transient pressure drop data across the riser during a solids flow cut-off experiment against its time derivative demonstrate the three distinct operating regimes that exist as the gas deplete the solid out of the riser. The transient was compared to data taken under steady state operations using statistically designed experiments. Results indicated that although there were significant differences when comparing operations in dilute conditions, there were no significant differences between the two methods in the fast fluidized and dense transport regimes. The transient method was capable of reproducing the solids circulation dependence on riser solids holdup and on the axial pressure profile. This transient method offers an accurate, easy, rapid, and reproducible means of characterizing CFB operations over a wide range of flow conditions. The lack of accuracy in the dilute regime is conjectured to be due to the wide particle size distribution that resulted in segregation during the transient testing. 相似文献